Pulse generator

ABSTRACT

A pulse generator comprises a trigger stage for periodically interrupting the operation of a plurality of parallel loads. Connected to a voltage supply, are a capacitor and a precision resistor connected between the loads and the supply, a switching unit receiving voltage peaks which appear at the precision resistor on an interruption of operation, the switching unit being responsive to the voltage peaks and retaining its switching state caused by a voltage peak at least until it receives a voltage peak of another value and means for variation of the frequency of interruptions in response to a switching state of the switching unit caused by a voltage peak of a value indicative of a field load.

I United States Patent [151 3,665,207 Sieber May 23, 1972 [54] PULSEGENERATOR 3,452,248 6/1969 Leeder ..340/8l [72] Inventor: Paul Sieber,Lortzingstrasse 20, 71 Heilg; S im: i

bronmBockinger, Germany 0 yo y [22] Filed: Aug. 25, 1970 PrimaryExaminer-H. 0. Jones Assistant Examiner-William J. Smith 21 A l. N 66782 1 DP 9 i Attorney-Spencer & Kaye [30] Foreign Application PriorityData [57] ABSTRACT Sept. 3, Germany ..P A ulse generator com rises atrigger stage for interrupting the operation of a plurality of parallelloads. Con- [52] US. Cl. ..307/l06, 340/81 R, 340/331 nected to avoltage Supply, are a capacitor and a precision [51] Int. Cl ..B60q 1/26sister connected between the loads and the supply a switching [58] FieldOf Search ..340/8 l 366, 331; 307/202, unit receiving voltage peakswhich appear at the precision 307/106; 328/9 10 sistor on aninterruption of operation, the switching unit being responsive to thevoltage peaks and retaining its switching [56] References cued statecaused by a voltage peak at least until it receives a volt- UNITEDSTATES PATENTS age peak of another value and means for variation of thefrequency of interruptions in response to a switching state of 3,329,8687/ 1967 Domann et al. ..340/8l the Switching unit Caused by a voltagepeak f a value 3,263,l l9 7/l966 Scholl 340/81 X tive ofafieldloa3,002,127 9/1961 Grontkowski. ...340/8l X 3,428,943 2/ 1969 Carp et a1...340/81 X 13 Claims, 2 Drawing figures PULSE GENERATOR BACKGROUND OFTHE INVENTION The present invention relates to a pulse generatorcomposed of a trigger stage for the periodically interrupted operationof a plurality of loads connected in parallel, particularly incandescentlamps.

In recent times, multiple transistorized circuits have been proposed forblinker systems in motor vehicles, which have the advantage of lowersusceptability to breakdown and timeconstant light and dark phases incomparison with the conventional relay blinker systems. It is the objectof the present invention to provide a particularly advantageous circuitfor a pulse generator which can be used preferably as a batterydrivenblinker unit or as a warning blinker system in vehicles of all kinds.

In the copending Patent application of Rudolf Gebhart and Paul Sieber,Ser. No. 85,038 filed on Oct. 29, 1970, and assigned to the assignee ofthe present application, it has already been proposed to provide aresistor which is so connected, between theload and the source of supplyvoltage, in the intervals between operation, that during the intervals,a constant measuring current flows through the loads and produces avoltage drop at the loads. This voltage drop is supplied to a switchwhich is so dimensioned that, during the intervals, in the event offailure of one or more loads, the switch changes its switching state incomparison with that with intact loads, as a result of the alteredpotential appearing at the switch in comparison with normal operationwith intact loads.

Thus this pulse generator which has already been proposed comprises acontrol unit which indicates whether the connected loads are intact orwhether one or more loads have failed and have to be replaced. It hasfurther been previously proposed that a voltage divider, which is sodimensioned that the charging voltage is reduced with intact loads,should be connected to the capacitor determining the intervals andoperating times, by means of the switch of the control unit in the eventof loads having failed.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide an improvement in the circuit for a pulse generator disclosed inthe above-mentioned co-pending patent application.

According to the present invention there is provided, a pulse generatorcomprising a trigger stage for periodically interrupting the operationof a plurality of loads connected in parallel. The trigger stageincludes a capacitor and a precision resistor connected between saidplurality of loads and a source of supply voltage for operating saidplurality of loads. A switching unit responsive to short voltage peaksand retaining the state caused by said voltage peaks at least until itreceives a voltage peak of a different value is provided with, means forconnecting said switching unit to said precision resistor for applyingthe voltage peaks which appear at said precision resistor oninterruption of the operation of said loads to said switching unit andmeans responsive to a state of said switching and caused by a voltagepeak indicative of a load failure for varying the rate of interruptionof the operation of said loads thus providing an inducation of loadfailure.

BRIEF DESCRIPTION OF THE DRAWINGS cordance with the invention, and

FIG. 2 is a diagram showing voltage behavior of various parts of thecircuit of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Basically in the circuitaccording to the invention, provision is made for the series connectionof a capacitor and a precision resistor to be connected between theloads and the source of supply voltage during the intervals inoperation, so that the voltage peaks appearing at the precision resistorwhen the load is switched off is applied to the control electrode of aswitching unit. The switching unit responds to short voltage peaks andretains the switching state which it assumed after the appearance of avoltage peak on disconnection, at least until a variation in potentialat one of its input electrodes is reached. The switching unit is sodimensioned and connected that, in the event of a reduced voltage peakon disconnection, caused by failing loads, it assumes a switching statewhereby a voltage divider is connected to a second capacitor of thetrigger stage, which determines the intervals in operation and theoperating times, in such a manner that the charging voltage of thesecond capacitor is reduced in comparison with its charging voltage forintact loads to an extent depending upon the voltage divider ratio, sothat the pulse repetition frequency of the generator is increasedaccordingly.

In the switching unit according to the invention, therefore, the controlunit is controlled dynamically with short time duration voltage peaks.This has the advantage that a measuring current only flows through theload for an extremely short time duration during the intervals inoperation. In this manner, the source of supply voltage is substantiallynot loaded by the additional power consumption of the control circuit.Furthermore, an additional increase in temperature is avoided in thehousing in which the blinker unit is accommodated.

In the circuit according to the invention, the switching unit preferablyconsists of a thyristor, the control electrode of which is connected tothe precision resistor. Instead of a thyristor, however, a bistabletrigger stage or another circuit storing information may be used.

A thyristor is a four-layer semiconductor component with three p-njunctions, the main electrodes generally being connected to the outerregions while one of the middle regions is provided with a controlelectrode. In the circuit according to the invention, a main electrodeof the thyristor is preferably connected to the center tap of a voltagedivider which is connected to the source of supply voltage through thecollectoremitter space of a tum-on transistor. The thyristor is sodimensioned that the bias voltage delivered by the voltage divider tothe main electrode of the thyristor, when the turn-on transistor isconducting, reliably ensures turning-on of the thyristor on the arrivalof a disconnection voltage peak. The magnitude of the disconnectionvoltage peak is determined by the total of the intact loads, whileturning on does not take place in the event of a reduced voltage peak ondisconnection caused by failed loads.

Referring now to FIG. 1, the circuit shown consists of two parts, thetrigger stage 1 and the indicating or control section 2. The twosections of the circuit are distinguished by broken lines.

The trigger stage consists of two transistors T, and T for example,n-p-n planar transistors. The emitter electrodes of these transistorsare at ground potential, while the collector of the transistor T, isconnected to the positive pole (for example 12 volts) of the sourcesupply voltage through the collector resistor R and the collector of thetransistor T is connected thereto through a relay winding R.Furthermore, the collector of the transistor T, is connected directly tothe base of the transistor T while the base series resistor R thecapacitor C, and the resistor R, are connected in series between thebase of the transistor T, and the collector of the transistor TConnected to the junction between the resistor R and the capacitor C, isa series connection of the resistor R the capacitor C, and the precisionresistor R which is connected to the positive pole of the source ofsupply voltage. The series connection of capacitor C and precisionresistor R is bridged by a switch 8,, which is actuated by the relay Rand which in turn is bridged by a resistor R, having a high resistance.The control section consists of a thyristor T,,, the control electrode GA of which is connected to the mid-connection between the capacitor C,and the precision resistor R The cathode K of the thyristor T, isconnected through a resistor R,,, to the ground electrode, while theanode A is connected to the midconnection of a voltage dividerconsisting of the resistors R, and R With the collector-emitter path ofa turn-on transistor T,, the voltage divider forms a series connectionwhich is connected between the poles of the source of supply voltage.The transistor T, is a transistor which is complementary to all theother transistors and its base electrode is connected to the collectorelectrode of the series transistor T,. The emitter electrode of thetransistor T, is connected to the ground electrode through an emitterresistor R The series transistor T, derives its base control potentialfrom the collector electrode of the transistor T of the trigger stage.The base electrode of a switching transistor T.,, the emitter electrodeof which is preferably at ground potential, is connected to thecollector or cathode electrode K of the thyristor T,,. In this manner,the voltage drop at the resistor R is the control voltage for thetransistor T The collector electrode of the transistor T, is connected,through a collector resistor R to the positive pole of the source ofsupply voltage, and is at the same time connected to the base electrodeof a series transistor T the emitter electrode of which is likewise atearth potential. The collector electrode of the transistor T isconnected to a resistor R, which, together with the resistor R, of thetrigger stage to which it is connected, forms a voltage divider. Theswitch 8,, can be connected to the loads through a further switch 8,. InFIG. 1, two loads L,, L, and L,, L, connected in parallel areillustrated as is usual in motor vehicles. The two possibleswitching-positions of the switch 8,, are bridged by an indicator lamp LThe circuit illustrated and described works as follows:

When the switch S is in the mid position, that is to say when no load isconnected to the pulse generator, a base current flows across theresistors R,,, R and R, to the transistor T,. As a result, thetransistor T, becomes conducting and its collector potential drops tothe collector saturation voltage which is lower than the base forwardvoltage of the transistor T The transistor T remains cut off. Thecapacitor C is charged to the value of the supply voltage. When loadsare connected up to the trigger stage 1 through the switch 5,, thepotential at the junction between the capacitor C and the resistor R,,,drops almost to ground potential because R, has a high resistance incomparison with the internal resistance of the load. Thus the potentialat the transistor T, also drops to such an extent that this changes overinto the cut-off stage. As a result, the collector potential risessharply at T, and changes the transistor T connected thereto over intothe conducting state. Thus a powerful current flows over thecollector-emitter path of T, through the relay winding R and closes theswitch S After the closing of S the loads are connected directly betweenthe poles of the source of supply voltage. If the loads are incandescentlamps, they will be illuminated. As a result of the dimensioning of theresistor R which bridges the switch S,,, the effect is achieved thatafter the closing of the switch 8,, the illumination phase of theconnected load begins.

Since the transistor T is conducting, the potential at the plate of thecapacitor C, connected to the resistor R, drops to the residual voltageof the transistor T Since the voltage cannot jump at the capacitor C,however, the other plate of the capacitor C, assumes the negative valueof the charging voltage and holds the transistor T, cut off. Thecapacitor is then charged, with the time constant 1-,=C. R from thisnegative voltage through the discharged state to positive voltagevalues. At a specific positive voltage, for example at 0.7 volts, thetransistor T, again becomes conducting and the transistor T cut off, therelay releases and the illumination phase is at an end. During thefollowing dark phase, a charge-exchange current flows across thecapacitor C, to the base of the transistor T, and maintains theconducting state of the transistor T, until the charge-exchange currenthas decreased to a value at which the transistor T, is again cut off andthe next illumination phase is introduced. When the transistor T,becomes conducting at the beginning of the dark phase, the capacitorcurrent of the capacitor C, jumps to the value I,,,,,,,==U,,/R, R,, inwhich U is the supply voltage. This current decreases to the value zerowith the time constant 1- =(R, R C,.

in H6. 2, the pulse pattern of the collector current at the transistor Tis illustrated in the upper most diagram. The potential at the collectorelectrode of the transistor T, also determines whether a thresholdvoltage permitting turning on is present at the thyristor T of thecontrol circuit 2 or not, while the control voltage for the thyristorT,, is derived from the junction between the capacitor C, and theprecision resistor R Since the relay has a certain, mechanicallydetermined response time, the signal supplied by the collector electrodeof the transistor T is always available before the control signalarrives at the thyristor. In this manner, the effects of chattering ofthe switch are eliminated and assurance is always provided that theresponse threshold at the thyristor T,, is set before the useful signalarrives at the control input 6,. When the relay contact S is opened, avoltage peak, which is proportional to the resistance of theincandescent lamps and dies away with the time constant C '(R R developsat the precision resistor R When the contact 8,, is closed, thecapacitor C is discharged across the precision resistor R and thevoltage at the capacitor C is added to the supply voltage U This voltagebehavior at the precision resistor R is illustrated in the bottomdiagram in FIG. 2. The section a shows the voltage behavior when bothloads connected in parallel are intact. If one load fails, the loadresistance increases by the factor 2 and there is a considerably lowervoltage peak on disconnection, as illustration in section b of thediagram. Calculation shows that the maximum difference between thevoltage peaks U and U is obtained when the precision resistor has thevalue R 12, {2 in which R, is the total resistance of two loadsconnected in parallel.

When positive potential is applied to the collector electrode of thetransistor T that is to say when the transistor T is cut off at thebeginning of the dark phase the transistor T, becomes conducting throughthe positive base potential. Thus T carries a collector current which,at the same time, is the base current of the complementary transistor T,which is thus likewise conducting.

Thus the voltage divider consisting of the resistors R, and R, isconnected between the poles of the source of supply voltage. Thisvoltage divider is so dimensioned that the potential taken off therefromand applied to the anode A of the thyristor T, is reliably sufficient,as a threshold voltage, when the voltage pulse arriving at the controlelectrode G, has its maximum value which is determined by all the intactloads to fire the thyristor T,,. On the other hand, if the voltage pulseon disconnection is reduced as a result of failed loads, this reduceddisconnection pulse is no longer sufficient for the firing of thethyristor. Starting with intact loads, therefore, during the dark phaseof the pulse circuit, a threshold voltage is applied to the thyristor asillustrated in the center diagram in FIG. 2. In addition, adisconnection pulse, which is sufficient for the firing, appears at thecontrol electrode G, of the thyristor at the begin-ning of the darkphase. As a result, a current which causes a voltage drop at theresistor R flows across the thyristor T, and the resistor R This voltagedrop controls the transistor T, so as to bring it into the conductingstate and the transistor T so as to bring it into the cut ofi state.Since T remains cut off during the dark phase withintact loads, theresistor R is ineffective.

At the beginning of the illuminated phase, the transistor T becomesconducting and the potential at the collector electrode of thetransistor T drops to a value at which the two transistors T and T arecut off. Thus the voltage divider consisting of the resistors R and R,is disconnected from the supply voltage and the thyristor T, is turnedoff.

If only small voltage pulses on disconnection, caused by one or morefailed loads, arrive at the control electrode G, of the thyristor T thethyristor is no longer turned on in the dark phases, substantiallyground potential then prevails at the base electrode of the transistorT, so that this transistor remains cut off and the transistor T isconsequently opened. As a result, the resistor R is connected to groundthrough the collectoremitter space of the transistor T In this case, thecapacitor C is only charged, at most, to the voltage U-U,,R /R R Themaximum capacitor charge-exchange current appearing in the dark phasesdrops, with the time constant T (R1 R1 R2 to the value zero from themaximum value Thus the pulse repetition frequency of the pulse generatorincreases. If the voltage divider R,, R, is so dimensioned that themaximum charge-exchange current and the maximum charging voltage of thecapacitor C are reduced by half in comparison with operation with intactloads, the pulse repetition frequency of the generator is doubled inconsequence. The indicator lamp L which connects the switch contacts ofthe switch S to one another will thus go on and off at twice as fast arate on the failure of one load; a striking and unerring sign of thefailure of a load. The pulse frequency of the generator can naturally bevaried in any other manner on the failure of loads, by appropriatedimensioning of the voltage divider R R Apart from the capacitors andthe incandescent lamps, all the components of the trigger stage and ofthe control circuit can be realized in the form of an integrated circuitby the thick-film, thin-film or integrated solid-state technique, on asemiconductor base. The pulse generator according to the invention can,of course, also be realized with the complementary transistors to FIG. 1if the polarity of the source of supply voltage is also alteredaccordingly. In order to operate the blinker circuit as a warningblinker system, all four loads are connected in parallel. Other loadsmay be used instead of lamps for other purposes.

It will be understood that the above description of the presentinvention is susceptible to various modifications changes andadaptations.

What is claimed is:

l. A pulse generator comprising a voltage supply, a trigger stage forperiodically interrupted operation of a plurality of loads connected inparallel, a capacitor and a precision resistor connected in seriesbetween said plurality of loads and said voltage supply during theoperating pauses of said plurality of loads, a switching unit responsiveto short voltage peaks and retaining the state caused by said voltagepeaks at least until said switching unit receives a voltage which isdifferent than a threshold voltage value, means for connecting saidswitching unit to said precision resistor for applying said voltagepeaks which appear at said precision resistor on interruption of theoperation of said loads to said switching unit, means for applying saidthreshold voltage to said switching unit, and means responsive to astate of said switching unit caused by a voltage peak indicative of aload failure for varying the rate of interruption of the operation ofsaid loads thus providing an indication of load failure.

2. A pulse generator comprising a voltage supply, a trigger stage forperiodically interrupted operation of a plurality of loads connected inparallel, a first capacitor for controlling the frequency of theinterrupted operation of said loads, a second capacitor and a precisionresistor connected in series between said plurality of loads and saidvoltage supply during the operating pauses of said plurality of loads, aswitching unit including an input electrode and a control electrode,said switching unit being responsive to short voltage peaks applied tosaid control electrode and retaining the state caused by said voltagepeaks at least until said input electrode receives a voltage which isdifferent than a threshold voltage value, means for connecting saidcontrol electrode of said switching unit to said precision resistor forapplying said voltage peaks which appear at said precision resistor oninterruption of the operation of said loads to said control electrode,means for applying said threshold voltage to said input electrode, avoltage d1- vider, and means responsive to a state of said switchingunit caused by a voltage peak indicative of a load failure forconnecting said voltage divider to said first capacitor for reducing thecharging voltage of said first capacitor depending on the ratio of saidvoltage divider to increase said frequency of said interruptions.

3. A pulse generator defined in claim 2, wherein said precision resistorhas a value substantially equal to the total resistance of two loads inparallel divided by the sqaure root of two.

4. A pulse generator defined in claim 2, wherein said switching unitcomprises a thyristor, the control electrode of which is connected bysaid connecting means to said precision resistor.

5. A pulse generator as defined in claim 4, wherein said thyristorfurther includes two main electrodes and wherein said generator furthercomprises a second voltage divider connected to said voltage supply, atap on said second voltage divider connected to one of said two mainelectrodes of said thyristor, a first transistor acting to turn on saidthyristor and having a collector-emitter path through which said secondvoltage divider is connected to said voltage, supply, said secondvoltage divider supplying a bias voltage to said thyristor whichensures, when said first transistor is conducting, that said thyristorfires on receipt of a voltage peak through said connecting means oninterruption of the operation of said loads when said loads are intact,and that said thyristor remains uneffected by the receipt of a voltagepeak on interruption of the operation of said loads when a failure exitsin said loads.

6. A pulse generator as defined in claim 5, further comprising a secondtransistor whose collector is connected to the base electrode of saidfirst transistor and a third transistor in said trigger stage, whosecollector is connected to the base electrode of said second transistor.

7. A pulse generator as defined in claim 6, further comprising a secondresistance connected between the other main electrode of said thyristorand the ground side of voltage supply, a fourth transistor which isconducting when said thyristor is conducting and to the base of whichthe voltage drop across said second resistance is applied, a fifthtransistor which is cut off when said fourth transistor is conductingand to the base of which one resistance of said first voltage divider isconnected so as to be connected to the ground side of said voltagesupply through said fifth transistor when conducting.

8. A pulse generator as defined in claim 7, wherein said firsttransistor is a p-n-p transistor and said second, third, fourth andfifth transistors are n-p-n transistors.

9. A pulse generator as defined in claim 7, wherein the circuit of saidpulse generator is an integrated solid state circuit.

10. A pulse generator as defined in claim 7, wherein the circuit of saidpulse generator is a thick film circuit.

11. A pulse generator as defined in claim 7, wherein the circuit of saidpulse generator is a thin film circuit.

12. A pulse generator as defined in claim 6, further comprising a relaywinding connected to the collector path of said third transistor forenergization when said first of said plurality of transistors isinducting, and a pair of make contacts operated by said relay winding anbridging said first capacitor and its associated resistance forconnecting said loads directly to said voltage supply when the contactsare made.

13. A pulse generator as defined in claim 12, further comprising a thirdresistance of high value bridging said make contacts.

1. A pulse generator comprising a voltage supply, a trigger stage forperiodically interrupted operation of a plurality of loads connected inparallel, a capacitor and a precision resistor connected in seriesbetween said plurality of loads and said voltage supply during theoperating pauses of said plurality of loads, a switching unit responsiveto short voltage peaks and retaining the state caused by said voltagepeaks at least until said switching unit receives a voltage which isdifferent than a threshold voltage value, means for connecting saidswitching unit to said precision resistor for applying said voltagepeaks which appear at said precision resistor on interruption of theoperation of said loads to said switching unit, means for applying saidthreshold voltage to said switching unit, and means responsive to astate of said switching unit caused by a voltage peak indicative of aload failure for varying the rate of interruption of the operation ofsaid loads thus providing an indication of load failure.
 2. A pulsegenerator comprising a voltage supply, a trigger stage for periodicallyinterrupted operation of a plurality of loads connected in parallel, afirst capacitor for controlling the frequency of the interruptedoperation of said loads, a second capacitor and a precision resistorconnected in series between said plurality of loads and said voltagesupply during the operating pauses of said plurality of loads, aswitching unit including an input electrode and a control electrode,said switching unit being responsive to short voltage peaks applied tosaid control electrode and retaining the state caused by said voltagepeaks at least until said input electrode receives a voltage which isdifferent than a threshold voltage value, means for connecting saidcontrol electrode of said switching unit to said precision resistor forapplying said voltage peaks which appear at said precision resistor oninterruption of the operation of said loads to said control electrode,means for applying said threshold voltage to said input electrode, aVoltage divider, and means responsive to a state of said switching unitcaused by a voltage peak indicative of a load failure for connectingsaid voltage divider to said first capacitor for reducing the chargingvoltage of said first capacitor depending on the ratio of said voltagedivider to increase said frequency of said interruptions.
 3. A pulsegenerator defined in claim 2, wherein said precision resistor has avalue substantially equal to the total resistance of two loads inparallel divided by the sqaure root of two.
 4. A pulse generator definedin claim 2, wherein said switching unit comprises a thyristor, thecontrol electrode of which is connected by said connecting means to saidprecision resistor.
 5. A pulse generator as defined in claim 4, whereinsaid thyristor further includes two main electrodes , and wherein saidgenerator further comprises a second voltage divider connected to saidvoltage supply, a tap on said second voltage divider connected to one ofsaid two main electrodes of said thyristor, a first transistor acting toturn on said thyristor and having a collector-emitter path through whichsaid second voltage divider is connected to said voltage, supply, saidsecond voltage divider supplying a bias voltage to said thyristor whichensures, when said first transistor is conducting, that said thyristorfires on receipt of a voltage peak through said connecting means oninterruption of the operation of said loads when said loads are intact,and that said thyristor remains uneffected by the receipt of a voltagepeak on interruption of the operation of said loads when a failure exitsin said loads.
 6. A pulse generator as defined in claim 5, furthercomprising a second transistor whose collector is connected to the baseelectrode of said first transistor and a third transistor in saidtrigger stage, whose collector is connected to the base electrode ofsaid second transistor.
 7. A pulse generator as defined in claim 6,further comprising a second resistance connected between the other mainelectrode of said thyristor and the ground side of voltage supply, afourth transistor which is conducting when said thyristor is conductingand to the base of which the voltage drop across said second resistanceis applied, a fifth transistor which is cut off when said fourthtransistor is conducting and to the base of which one resistance of saidfirst voltage divider is connected so as to be connected to the groundside of said voltage supply through said fifth transistor whenconducting.
 8. A pulse generator as defined in claim 7, wherein saidfirst transistor is a p-n-p transistor and said second, third, fourthand fifth transistors are n-p-n transistors.
 9. A pulse generator asdefined in claim 7, wherein the circuit of said pulse generator is anintegrated solid state circuit.
 10. A pulse generator as defined inclaim 7, wherein the circuit of said pulse generator is a thick filmcircuit.
 11. A pulse generator as defined in claim 7, wherein thecircuit of said pulse generator is a thin film circuit.
 12. A pulsegenerator as defined in claim 6, further comprising a relay windingconnected to the collector path of said third transistor forenergization when said first of said plurality of transistors isinducting, and a pair of make contacts operated by said relay winding anbridging said first capacitor and its associated resistance forconnecting said loads directly to said voltage supply when the contactsare made.
 13. A pulse generator as defined in claim 12, furthercomprising a third resistance of high value bridging said make contacts.